Neutron Resonance Spectroscopy. X.Th232andU238

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Abstract
Neutron time-of-flight spectroscopy measurements were made for a range of sample thicknesses of Th232 and U238 using the Nevis synchrocyclotron. These included transmission measurements using 200- and 40-m paths, self-indication measurements at 40 m, and Moxon-Rae capture measurements at 33 m. Resonance energies and Γn values were obtained for n=302 levels in Th232 to 4.0 keV and 269 levels in U238 to 4.6 keV, with essentially no missed s levels and inclusion of a significant number of p levels. Γγ values were obtained for 84 levels in Th232 and 71 in U238 to 2400 eV, with 〈Γγ〉=[21.2±0.3 (stat.)±0.9 (syst.)] meV (Th232) and [22.9±0.5 (stat.)±0.9 (syst.)] meV (U238). In both cases a χ2 analysis gives ∼100 degrees of freedom including the effects of measurement errors. The values for the resonance energies were obtained from the data before the analysis was completed for Γn and Γγ values. The division of the levels into s and p populations, described in detail elsewhere, was made to achieve a "best" fit to many statistical tests relating to the orthogonal-ensemble theory for single level populations, with a resulting good fit to numerous tests. For the chosen s level population, 104 S0=(0.84±0.08) for Th232 and (1.08±0.10) for